Observation of second-harmonic generation in an oriented glassy nematic phase of a closo-decaborane derivative

The optical second-harmonic generation(SHG) and the linear optical properties were investigated in a planar cell containing aligned nonchiral nematic derivative of B₁₀H₁₀²⁻: 1-(4-heptyloxypyridin-1-yl)-10-(4-pentyl-1-thiacyclohexyl)-closo-decaborane (HPTD) as a function of temperature. The compound showed a low level of the SHG signal in the polycrystalline state, and no nonlinear optical effect was detected in the fluid nematic state (N) either in the presence or absence of an orienting electric field. When frozen, the resulting thermodynamically unstable nematic glassy phase (glassyN) unexpectedly exhibited the second-order nonlinear optical properties, implying a partial polar order in the arrangement of the in-plane-aligned molecules in a liquid-crystal cell. The efficiency of the SHG was analyzed for two polarization configurations yielding the main component of the second-order nonlinear susceptibility χₓₓₓ(²)=2.3±0.3pmV⁻¹ along the nematic director x. A comparison of the experimental susceptibility with a hypothetical one estimated from the vectorial component of the molecular hyperpolarizability showed a relatively low degree of the spontaneous polar order. The dispersion of the principal refractive indices in the glassy state of HPTD was derived from dichroic absorption spectra using an interference fringe method and fitted with a Sellmeier-type equation. At 527nm the birefringence of HPTD is Δn=0.31.The authors acknowledge the Australian Research Council Discovery Project No. DP0556942 and the NSF Grant No. DMR-0111657 for financial support

Biopolymer-based material for optical phase conjugation

We present results of optical phase conjugation experiments in modified DNA (deoxyribonucleic acid) - dye system. The system consisted of a biopolymeric matrix made of DNA blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride (CTMA) and doped with a photochromic dye Disperse Red 1. Results were obtained in a typical degenerate four wave mixing experiment. For sample excitation we used linearly polarized light at a wavelength 514.5 nm, delivered by an argon ion (Ar+) laser. The phase conjugated signal which emerged from the sample had rise and fall time constants of a few milliseconds with an excellent reversibility

Amplified spontaneous emission in the spiropyran-biopolymer based system

Amplified spontaneous emission (ASE) phenomenon in the 6-nitro-1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indolin] organic dye dispersed in a solid matrix has been observed. The biopolymer system deoxyribonucleic acid blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride served as a matrix. ASE appeared under sample excitation by UV light pulses (λ=355 nm) coming from nanosecond or picosecond neodymium doped yttrium aluminum garnet lasers and has been reinforced with green (λ=532 nm) light excitation followed UV light pulse. The ASE characteristics in function of different excitation pulse energies as well as signal gain were measured

Deoxyribonucleic acid-based photochromic material for fast dynamic holography

The authors report on a biopolymeric material made of deoxyribonucleic acid (DNA) complexed with the cationic surfactant cetyltrimethyl-ammonium (CTMA) and doped with the photochromic disperse red 1 dye (DR1) for dynamic holographic recording. The molar ratio of the DNA-CTMA to the dye is about 5:1. They have found that the photochromic properties of DR1 in the DNA-CTMA matrix are favorably modified in speed of response with respect to conventional polymeric matrices. Dynamic holographic gratings which were inscribed in DR1:DNA-CTMA films are characterized by switching times within a 1–10ms range. An excellent reversibility of the recording process is reported.The authors acknowledge the Australian Research Council Discovery Project No. DP0556942, the Materials and Manufacturing Directorate Air Force Office of Scientific Research, the AOARD Grant No. 05-4010, and the Polish Ministry of Science and Higher Education Grant No. N50713231/3302 for financial support

Thermocapillary marangoni flows in Azopolymers

It is well known that light-induced multiple trans-cis-trans photoisomerizations of azobenzene derivatives attached to various matrices (polymeric, liquid crystalline polymers) result in polymer mass movement leading to generation of surface reliefs. The reliefs can be produced at small as well as at large light intensities. When linearly polarized light is used in the process, directional photo-induced molecular orientation of the azo molecules occurs, which leads to the generation of optical anisotropy in the system, providing that thermal effects are negligible. On the other hand, large reliefs are observed at relatively strong laser intensities when the optofluidization process is particularly effective. In this article, we describe the competitive thermocapillary Marangoni effect of polymer mass motion. We experimentally prove that the Marangoni effect occurs simultaneously with the optofluidization process. It destroys the orientation of the azopolymer molecules and results in cancelation of the photo-induced birefringence. Our experimental observations of polymer surface topography with atomic force microscopy are supported by suitable modelings

Amplified spontaneous emission of Rhodamine 6G embedded in pure deoxyribonucleic acid

Deoxyribonucleic acid (DNA) is commonly viewed as a genetic information carrier. However, now it is recognized as a nanomaterial, rather than as a biological material, in the research field of nanotechnology. Here, we show that using pure DNA, doped with rhodamine 6G, we are able to observe amplified spontaneous emission (ASE) phenomenon. Moderate ASE threshold, photodegradation, and reasonable gain coefficient observed in this natural host gives some perspectives for practical applications of this system in biophotonics. Obtained results open the way and will be leading to construction of truly bio-lasers using nature made luminophores, such as anthocyanins